To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, a self-aligned double patterning (SADP) process involving the steps of forming a resist pattern by ArF lithography, growing a film on opposite sides of pattern features, and forming two pattern features with a half line width from one resist pattern feature is utilized to manufacture 20-nm node devices on a mass scale. One candidate for the microprocessing technology for manufacturing 10-nm node devices of the next generation is a self-aligned quadruple patterning (SAQP) process involving repeating twice the SADP process of ArF lithography patterning. However, the SAQP process is believed very expensive in that formation of sidewall film by CVD and subsequent processing by dry etching must be repeated many times. The EUV lithography of wavelength 13.5 nm is capable of forming a pattern with a 10-nm size via a single exposure step, but suffers from low productivity because the laser power is yet low. As a way out of the deadlock of the miniaturization technology, the development of 3D devices such as vertically stacked flash memories typically BiCS is in progress, but this process is also expensive.
Toward the goal of double resolution, studies are made on the exposure technology and resist material. If first exposure is followed by second exposure at a half-pitch shifted position, the optical energy of second exposure offsets the optical energy of first exposure so that the contrast becomes zero. If a contrast enhancement layer (CEL) is formed on the resist film, the incident light to the resist film becomes nonlinear so that the first and second exposures do not offset each other. Thus an image having a half pitch is formed. See Non-Patent Document 2. It is expected that similar effects are produced by using an acid generator capable of two photon absorption to provide a nonlinear contrast. Using this double imaging method, the resolution can be doubled through two exposure steps and a single development.
A resist material having both positive and negative properties has been proposed. This resist material displays the positive tone response that it is substantially insoluble in alkaline developer where it receives a low exposure dose, but increases its alkaline dissolution rate as the exposure dose is increased, and the negative tone response that it starts reducing its alkaline dissolution rate as the exposure dose is further increased. Lithographic processing of such a positive/negative resist material can produce a resolution twice that of the mask pattern since those portions of resist film having received low and high exposure doses are left after development. Known positive/negative resist materials include a positive/negative hybrid resist composition obtained by adding a crosslinker to a positive resist material as described in Patent Document 1 and Non-Patent Document 3, and a positive/negative hybrid resist composition utilizing competitive positive and negative reactions in the co-presence of a benzyl alcohol and an acetal acid labile group as described in Patent Document 2. Patent Document 3 discloses a positive/negative hybrid resist composition having both an acid generator and a base generator added thereto. As the exposure dose increases, the acid generator having a high generation efficiency generates acid so that positive response manifests via deprotection, whereas a region receiving an increased exposure dose displays negative response because the base generator having a low generation efficiency generates an amount of base surpassing the amount of acid so that deprotection reaction may not occur.
The positive/negative hybrid dual-tone resist composition permits a pattern to be formed at a double resolution by an ordinary process involving single exposure and single development.